Fix package resolving in webpack projects

[susnux]

Currently the 4.0.0 release can not be used with webpack projects, because they will throw:
ReferenceError: exports is not defined.

Webpack tries to resolve the import of @nextcloud/dialogs to node_modules/@nextcloud/dialogs/dist/index.js.
This is a commonjs file, but webpack expects an esm file, so exports is not defined.

I guess this happens because dialogs has its type set to module´ so every .js` file within will be handled as esm.

So to fix this we need to explicitly name commonjs files .cjs.

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I noticed this issue when trying to use @nextcloud/vue 7.6.0 which depends on dialogs version 4.0.0.

[mejo-]

I can verify that this fixes using @nextcloud/vue 7.6.0.

[juliusknorr]

Thanks @susnux I'll spin a new release

[juliusknorr]

Building at https://github.com/nextcloud/nextcloud-dialogs/actions/runs/4193918096